• Travel with a cheap burner phone.
• Just before returning change your password to a long randomly generated string of letters and numbers.
• Write it down and mail it your home address.
• Lock your phone when you arrive at customs.
• Tell border agents what you did and that you can't unlock it until you get your letter next week.

Thus they only have 2 options: A. Seize it and have the lab unlock a burner with nothing on it. B. Or they can just let it go. In either case they're suckers wasting their own time instead of yours.